Subcutaneous Migration: A Dynamic Anatomical Study of Gluteal Fat Grafting.

Background: Recent anatomical studies have demonstrated that fat placed subjacent to the fascia of the gluteus maximus muscle can migrate deep through the muscle into the submuscular space, possibly causing tears in the gluteal veins, leading to fat embolisms. The purpose of this study was to define and to study subcutaneous migration and to determine whether fat placed in the subcutaneous space under a variety of pressures and fascial integrity scenarios can indeed migrate into the deep submuscular space.

Methods: Four hemibuttocks from two cadavers were used. Proxy fat was inserted using syringes with various fascia scenarios (1: fascia intact; 2: cannula perforations; 3: 6mm fascia defects) or using expansion vibration lipofilling (4: fascia intact). Subcutaneous pressures were recorded. After injections, anatomical dissections were performed to evaluate the migration of the proxy fat for each of the scenarios.

Results: Scenario 1: pressure reached approximately 125 to 150 mmHg and then plateaued and all the proxy fat remained in the subcutaneous space. Scenario 2: pressure reached a 199-mmHg plateau and no proxy fat spread deeper into the muscle or beneath it. Scenario 3: pressure gradually rose to 50 mmHg then fell again and the submuscular space contained a significant amount of proxy fat. Scenario 4: pressure rose to a maximum of 30 mmHg and all of the proxy fat remained in the subcutaneous space.

Conclusions: The gluteus maximus fascia is a stout wall that sets up the dangerous condition of deep intramuscular migration with subfascial injections and the protective condition of subcutaneous migration with suprafascial injections. These persuasive findings are profound enough to propose a new standard of care: no subfascial or intramuscular injection should be performed, and all injections should be performed exclusively into the subcutaneous tissue.